1. Field of the Invention
The present invention generally relates to a method of controlling a start-up of a motor, and more particularly to a method of controlling a start-up of a motor used for rotating a disk installed in a disk apparatus, which motor does not have an angular position sensor.
2. Description of the Related Art
In recent years, sensorless motors have been used for magnetic disk apparatuses used as an external memory apparatus because of the requirements for large capacity, high speed processing, low price and small size, the sensorless motors being used for driving a spindle for a magnetic disk. These magnetic disk apparatuses may have a standby mode function by which rotation of the sensorless motor is temporarily stopped when an access command is not input for a predetermined period of time so as to cut off unnecessary power consumption by the sensorless motor so that a low power consumption is achieved.
Accordingly, when the access command is input, the sensorless motor must be started up, first, to reach a steady rotational speed, and thus it is required to reduce the period of the start-up time of the sensorless motor.
A description will now be given, with reference to FIG. 1, of a conventional magnetic disk apparatus. FIG. 1 is a plan view of a conventional magnetic disk apparatus 11.
As shown in FIG. 1, the magnetic disk apparatus 11 comprises an actuator 12 having an arm 13 on one end of which is provided a magnetic head 14 via a support spring 13a. A base part of the arm 13 is rotatably supported by a pivot 15.
At the other end of the arm 13 relative to the pivot 15 a rotational support portion provided with a coil 17 is formed. Two magnets 18a and 18b are situated under the coil 17. The coil 17 and the magnets 18a and 18b constitute a voice coil motor (VCM).
The arm 13 of the actuator 12 rotates about the pivot 15 when an electric current is supplied to the coil 17 from a printed circuit board 21 via a flexible printed circuit board 22. Accordingly, the magnetic head 14 is moved along a radial direction of a magnetic disk 20 attached to a spindle 19 which is rotated by a sensorless-type spindle motor (not shown in the figure). When the magnetic disk 20 is rotating, the magnetic head 14 floats on the magnetic disk 20 due to an air flow generated by the rotation of the magnetic disk 20.
It should be noted that the sensorless-type motor is used for rotating the magnetic disk 20 because it is difficult to reserve a space to provide a sensor due to the requirement for a small and thin apparatus.
Additionally, a controlling circuit board (not shown in the figure) is provided which comprises a central processing unit (CPU), a micro processor unit (MPU), a read/write controlling unit, a head positioning unit and a spindle motor controlling unit.
FIG. 2 shows a side view of a portable personal computer 23 in which the magnetic disk apparatus shown in FIG. 1 is used. The portable personal computer 23 comprises a main body 24 having an operational unit 24a and a lid 25 having a display unit 25a. The above-mentioned magnetic disk apparatus 11 is inserted into the main body 24 from a side thereof. In this state, a host computer in the main body 24 is connected to the CPU in the magnetic disk apparatus 11 via a SCSI interface so that commands and data are transmitted therebetween.
Additionally, in apparatuses like the above-mentioned portable personal computer 23, it is common to have a battery for a power source, and thus to have a function for reducing power consumption. More specifically, an operation of the spindle motor of the magnetic disk apparatus 11 is stopped when an access request is not sent from the host computer for a predetermined period of time in a state where the magnetic disk apparatus 11 is not operated. The spindle motor is started when the access request is received.
FIG. 3 is a flow chart of a start-up operation of the spindle motor from a standby mode. First, a spin-on command is sent, in step 51 (hereinafter step is abbreviated as ST), to the spindle motor controlling unit from the MPU when an access request is sent to the CPU of the magnetic disk apparatus 11 from the host computer. An aligning operation of a stator and a rotor of the spindle motor is then performed in ST52. These steps normally take 2 to 3 seconds.
The aligning operation is performed for supply an electric current to a predetermined phase of the spindle motor so as to fix the position of the rotor relative to the stator. This aligning operation is necessary for the sensorless-type spindle motor which does not have a sensor to detect an angular position of the rotor.
Thereafter, a synchronization control is performed, in ST53, to forcively apply a rotating magnetic field until a rotational speed of the spindle motor reaches a speed at which a back electromotive force (BEMF) can be detected. A BEMF signal is then detected, in ST54, by a BEMF detection control, and the spindle motor is operated, in ST55, at a predetermined steady rotational speed by applying power to a correct phase.
On the other hand, when the spindle motor is not operated, the magnetic head 14 is in contact with the magnetic disk 20. If this condition continues for a long period of time, the magnetic head adheres to the magnetic disk 20. In order to eliminate this problem, a measurement is taken at a delivery stage for an adhesion torque under a predetermined condition. For example, a relationship between an applied voltage and a torque is obtained beforehand, and the adhesion torque is measured by gradually increasing the voltage applied to the spindle motor.
However, in the case where the spindle motor is started up from the standby mode as mentioned above, the aligning operation is needed as an angular position of the rotor is not fixed. Accordingly there is a problem in that time must be spent on the alignment operation before the rotational speed of the spindle motor reaches a steady speed from the time a start-up command is received. This is a common problem with inventions described in Japanese Laid-Open Patent Applications No. 4-109891 and No. 4-109892 in which a reduction of a start-up time until the rotational speed becomes steady is disclosed.
Additionally, as described in Japanese Laid-Open Patent Application No. 5-290500, it is known to reduce the start-up time by means of a detection of an angular position of the spindle motor in accordance with information recorded on a predetermined position of the magnetic disk attached to the spindle. However, there is a problem in that the recorded information on the magnetic disk may be lost for some reason, and thus reliability is not ensured.
There is another problem in that when the adhesion torque is measured, in a case where the aligning operation of the spindle motor is performed, there is a possibility that the spindle motor will rotate in a reversed direction, and thus an accurate measurement cannot be performed.